SiC has been the subject of interest as a substrate material as a successor of Si for a next-generation power device. However, existing SiC contains many dislocations, which greatly affect device characteristics, compared with Si. Hence, various proposals have been made on a technique that decreases dislocations in a SiC single crystal.
For example, Patent Literature 1 discloses a technique where a conical seed crystal, of which the central axis direction is within plus or minus 10 degrees from the <0001> direction and the vertical angle is 20 degrees to 90 degrees, is used in order to decrease micropipes and screw dislocations in a grown crystal.
Patent Literature 2 discloses a technique where crystal growth is repeated with a growth plane provided with an offset angle of 20 degrees or more from a {0001} plane.
Furthermore, Patent Literature 3 proposes a technique where a seed crystal, of which the growth plane is processed in shape such that an offset angle of the growth plane is decreased along a direction from a lower part of a {0001} plane to a highest part of the {0001} plane on the growth plane, is used to prevent a dislocation flow from an offset upstream portion into an offset downstream portion.
To improve device characteristics, dislocations in a crystal are desirably decreased as possible. On the other hand, not only overall reduction of dislocations in the SiC single crystal, but also a technique of grouping dislocations into specific dislocation types or into specific Burgers vectors is also considered to be an effective approach for improving device characteristics.
Dislocations in SiC include screw dislocation, edge dislocation, and basal plane dislocation. There has been reported influence of each dislocation type on a device, such as an increase in leakage current caused by a threading dislocation such as a screw dislocation and an edge dislocation, and forward degradation of a bipolar device caused by a basal plane dislocation. Thus, if a SiC single crystal, in which a specific dislocation type is reduced, can be manufactured, and when the SiC single crystal is used in correspondence to a type of a device to be fabricated, a characteristic as an issue of that device can be improved.
In a previous attempt, basal plane dislocations in a substrate are converted into edge dislocations at an increased rate during epitaxial growth. Such an attempt, however, has not achieved conversion of all basal plane dislocations into edge dislocations. One possible reason for this is as follows. A plurality of Burgers vector directions exist in the basal plane dislocations, and a basal plane dislocation having a Burgers vector parallel to an offset direction of the substrate is difficult to be converted into edge dislocation.
Thus, it is considered that when a substrate, which mainly contains basal plane dislocations having a Burgers vector in a specific direction (i.e., contains no basal plane dislocation having a Burgers vector parallel to the offset direction), is fabricated, conversion efficiency of basal plane dislocations into edge dislocations can be improved.
However, a specific technique where a SiC single crystal is grown so as to mainly contain a specific dislocation type, or a specific technique where a SiC single crystal is grown so as to exclusively contain a specific Burgers vector has not been known. In addition, there has been no attempt of exclusively forming, in a wafer surface, a specific dislocation type or a dislocation type having a specific Burgers vector in a specific region.